1. Field of the Invention
The present invention relates to a charge-injected internal combustion engine equipped with a charge injection valve, for injecting a premixed air-fuel charge into a combustion chamber. More particularly, the present invention relates to a charge-injected internal combustion engine in which combustion air is compressed by an air pump driven by the engine crankshaft.
2. Background Art
A limited number of charge-injected internal combustion engines have previously been known. For example, a charge-injected engine is disclosed in Japanese Patent Publication No. 2000-514150. This internal combustion engine is equipped with an air-fuel injection unit for injecting a premixed air-fuel mixture directly into a combustion chamber, and an air compressor is driven by the engine crankshaft, in order to provide compressed air for the air-fuel injection unit.
In the engine described in the reference, fuel is mixed with compressed air from the air duct within the air-fuel injection unit, and the air-fuel mixture is injected into the combustion chamber. An internal combustion engine with good combustibility is therefore obtained, because a powerful airflow is formed, due to the injected compressed air, so as to promote atomization of the fuel.
However, at the time of starting up the internal combustion engine described in Japanese Patent Publication No. 2000-514150, and in particular, directly after the beginning of engine startup, the volume of compressed air discharged from the air compressor is small. Therefore, when the pressure of the compressed air within the air duct falls to ambient pressure, due to the internal combustion engine having been stopped for a long time, it is not possible to quickly provide compressed air at a sufficient pressure to convey the fuel within the cylinder.
Because the air flow of compressed air to the fuel injection unit is weak, it becomes difficult for the fuel to be atomized, combustibility falls, and starting performance is therefore lowered.
The internal combustion engine of Japanese Patent Document 2000-514150 opens a valve of the fuel injection unit of a cylinder on a compression stroke at the time of starting up, and increases the air pressure within the air cylinder by guiding compressed air to the fuel injection unit.
However, in the related technology, when the engine has not yet reached operating speed, compressed air at the time of the compression stroke bleeds outwardly from the cylinder via the fuel injection unit. The pressure within the cylinder therefore falls, and the starting performance of the internal combustion engine deteriorates. Further, it is necessary to control the timing of valve opening of the fuel injection unit, in order to increase the air pressure within the air duct. Control of the fuel injection unit therefore becomes complex, and cost is increased, in cases where a pressure sensor is required to detect the pressure within the intake air duct. Moreover, as there is a small amount of oil mixed in with the air within the cylinder bore, when the compressed charge from the cylinder bore flows outwardly from the cylinder in the reverse direction from normal flow, this oil adheres to, or accumulates as a deposit on the walls of an air passage within the fuel injection unit, and interferes with the flow of the compressed air.
Although the known charge-injected internal combustion engines are useful for their intended purposes, a need still exists in the art for a charge-injected internal combustion engine having improved startup operation. A need also exists for a charge-injected internal combustion engine having improved fuel efficiency.